This invention relates to the completion of wells by lowering a perforating gun on tubing through a packer previously set in the casing, the packer typically being a permanent or other heavy duty packer suitable for a high pressure, high temperature environment, the packers being run in on a wire line or tubing.
The completion of wells is known to those skilled in the art as evidenced by the following patents: Vann U.S. Pat. No. 3,706,344; Vann, et al. U.S. Pat. No. 3,871,448; Vann U.S. Pat. No. 3,966,236; and Vann U.S. Pat. No. 4,066,282.
In carrying out the above completion techniques, it is advantageous to employ a packer actuated vent assembly, such as disclosed in some of the above patents; and perforating guns, such as disclosed in the above mentioned U.S. Pat. No. 3,706,344 as well as U.S. Pat. No. 4,140,188. Various different packers, including permanent packers, are known such as described in the 1974-75 Baker Catalog, Sections III, IV and V; Baker Oil Tools, Inc., Edition of the Composite Catalog of Oil Field Equipment and Service, published by The Gulf Publishing Co., Houston, Tex., See also Volume 1, of the 1980-81 Edition of the Composite Catalog of Oil Field Equipment and Services, pages 640-772, referring to Baker Packer Completions Services' Packer Systems.
It is essential for safety reasons that control be maintained over deep, high temperature, high pressure wells. Such a well might be over 10,000 feet deep, have a bottomhole temperature of about 300.degree. F., and a bottomhole pressure of over 5,000 psi. Such control is initially maintained by a hydrostatic head and then later maintained by setting a permanent packer in the cased borehole. One object is to prevent any blowout of the well. A replacement of the mud with a lighter clean fluid prior to the setting of a permanent packer may remove the margin of safety. Thus, it is desirable to keep heavy mud in such a well for as long as possible to insure that the production zone is killed. Once the packer has been set and the cased borehole can be sealed off, the margin of safety is insured. A hydrostatic head is still maintained in the annulus above the packer. A permanent packer is almost always used in a deep, hot, high pressure well. A permanent packer will contain and withstand the temperatures and pressures of such a well since a permanent packer is a more heavy duty packer. Thus, very few customers will permit a retrievable packer in such a well where a retrievable packer is mounted on a tubing string with a perforating gun. For example, a retrievable packer might fail after the mud was removed with a lighter fluid in the tubing string or where the tubing string was swabbed dry in preparation for perforation. A retrievable packer, mounted on a tubing string with a perforating gun, is generally considered inadequate to control a well of this environment.
The permanent packer may be run into the well alone or suspending a perforating gun. Casing size is one of the principal factors determining whether a permanent packer suspending the perforating gun or a permanent packer alone is run and set in the well. Where the cased borehole has at least a 7 inch casing, the permanent packer can have an internal bore with an internal diameter of 4 inches. A 4-inch packer bore will permit the lowering of a sufficiently large sized perforating gun to provide adequate perforations. Thus, the packer bore size dictates the maximum sized perforating gun which can be used in the well when the gun is lowered into the well after the packer is set. If the casing has an interior diameter of less than 7 inches or even if the casing is a 7-inch casing but a big perforating gun is required, it would be necessary that the perforating gun be suspended below the packer. Such a system is described in patent application Ser. No. 384,508 filed June 3, 1982, entitled "Gun Below Completion Tool String" invented by Brieger, George and Colle.
Although an apparatus such as disclosed in the Brieger, George, and Colle application may be used to suspend the gun from the permanent packer, it is more desirable to lower and set the permanent packer within the well where the packer does not support the perforating gun. Running the permanent packer alone into the well on a wireline is a more reliable and simpler method. Running the permanent packer alone is less complicated and a more desirable system than a permanent packer suspending the perforating gun. Further, if anything goes wrong after the packer and gun have been run, there is an opportunity to not run the gun or remove the gun from the hole. If a permanent packer suspending the gun had been run, then it would be necessary to unset the packer which may require either drilling or milling to remove the packer or an attempt to fish the packer for retrieval. Further, where the gun is suspended below the packer, the packer is set and a separate tubing string must be run into the well for circulation and detonation of the gun. Although running the permanent packer into the well with a wireline is preferred, a tubing string could be used. However, the use of a tubing string would require an extra trip into the well.
Generally, there is little problem lowering the permanent packer on a wireline even though the well is full of drilling mud. The permanent packer is permitted to more or less fall-feed itself and settle into the well on the wireline. Where lowering the permanent packer on a wireline becomes a problem, generally the permanent packer is pulled out of the hole and the mud is reconditioned to the point where the permanent packer will lower itself on a wireline into the well. However, the reconditioning of mud lasts only a short period of time and it is necessary to pull the permanent packer, recondition the mud, and lower the permanent packer to the desired position quickly.
Although the environment just described for the present invention has been in relation to the use of a permanent packer, there are applications where the present invention could be used with a retrievable packer, such as in the case of a recompletion. For example, where squeeze perforations have been performed, the old perforations are plugged by setting a packer and pumping cement down into the well and into any open performations. The cement is squeezed back into the formation to plug all the holes. Where the old well still has a fairly high pressure and a water column is not sufficient to keep it killed, it is often desired to have a hydrostatic head of drilling mud in the tubing string suspending the perforating gun to be sure that there is no release of any of the hydrostatic head off of the squeezed perforations until a packer is set for making new perforations. Thus, the well includes drilling mud from the production zone to the surface to insure protection against a blowout or to insure there is no breakdown of the squeeze perforations until everything is prepared to create new perforations. The above is one example of why mud might be permitted in the tubing string while running a retrievable packer and perforating gun into the well.
Where the tubing string may be left in the hole for a long period of time prior to completing the well in the above-described applications, the surrounding mud often contaminates the interior of the tool. The heavy particles of mud and other suspended matter gravitate toward the bottom of the tool string where the contaminant densifies into a heavy layer of material. The longer the tool string is left downhole, the more the drilling mud is permitted to settle and congeal. In a perforating gun having a bar actuated gun firing head, for example, it is possible for the mud to densify about the gun firing head mechanism and become compacted and viscous to such an extent that the gun firing head cannot be impacted and detonated. The firing mechanism requires 20 ft-lbs of impact for detonation. Where the mud is permitted to settle and congeal, it may well be impossible to attain 20 ft-lbs of impact from the bar.
It is often desirable to complete the well at some subsequent time and the downhole may be left dormant. For example, one may wish to leave the downhole dormant until one is prepared to complete several wells and tie them all in at one time. However, during such an interval, the heavy particles of the mud and other suspended matter gravitate toward the bottom where the contaminants density into a heavy layer of material. The longer the time period, the more the drilling mud is permitted to settle and congeal. Thus, it is possible for the mud to densify in the lower portion of the hole and become compacted. Thus, it is desirable to circulate into a well to remove compacted and congealed material therein.
The well fluid often includes extremely heavy mud, much like clay, which fills the lower end of the cased wellbore. When the tool string is run into the hole, mud enters the vent port and is displaced back up the tubing string. When a firing mechanism, such as a bar, is subsequently dropped downhole in order to complete the well, the downwardly traveling bar encounters the heavy mud and is decelerated. Sometimes the mud and other debris is so dense the bar cannot penetrate the stratified material.
The problem of contamination is compounded when the perforating tool string is left downhole for any substantial length of time. Accordingly, it would be desirable to have made available a perforating tool string which can be manipulated in a manner whereby the lower borehole annulus is cleaned by displacement of the heavy debris-laden well fluid with cleaning fluid, as for example fresh clean oil, fresh water, or salt water. The elimination of the contaminants from the lower borehole greatly enhances the operation of the perforating gun device.
The well completion method and apparatus of the present invention overcomes the problems of the above applications by preventing mud and debris from collecting around the firing mechanism and permitting circulation for the removal of any mud and debris. Because circulation is desired in the case of a permanent packer and because a hydrostatic head may be desired in the tubing string in the case of a retrievable packer, the tubing string of the present invention is run into the well open permitting the string to completely fill up with drilling mud as it is run into the well.
During completion of a well, where a permanent packer is installed downhole in the borehole and a packing mandrel is seated within the packer, it is necessary for provision to be made for flow to occur from the lower to the upper annulus during the seating of the packer mandrel because of the incompressibility characteristics of the well fluids. It is undesirable for the lower annulus to be vented directly into the tubing string, because the contaminated well fluid is translocated from the lower annulus directly into the tubing string where the contaminates gravitate in a downward direction and obscure the gun firing head mechanism.
In some permanent completion apparatus, it is sometimes desirable to run a dry, clean tubing into the borehole. However, when a dry tubing is run into the borehole, the packer set, and a vent assembly subsequently opened, the annulus fluid is no longer fully closed off so that the flow of additional fluid from the formation into the annulus is resisted only by the hydrostatic head in the tubing. Consequently, if the formation pressure exceeds the hydrostatic head an appreciable amount, it is possible to lose control of the well when the shaped charges of the gun are exploded, releasing formation pressure to the annulus.
In the case of a permanent packer, the present invention has the advantage that the simpler and less complicated method of running the permanent packer into the well alone on a wireline can be used, the permanent packer can be set without making an additional tubing run, the perforating gun assembly is not permanently attached below the permanent packer so that it can be removed easily from the well if problems arise, and the tool string with perforating gun and circulation apparatus can all be lowered into the well at one time. Once on location for perforation, after the well has been cleaned and the well is ready to be flanged up and the gun detonated, circulation is permitted down to the firing mechanism of the perforating gun so that there is no level of mud extending in the casing above the perforating gun. However, the present invention permits any desired amount of the mud or any other fluid to remain in the well for safety, the permanent packer can be run in and set independent from the rest of the tools, circulation can occur as the perforating gun is being lowered into the well, and then the tubing string can sting through the packer in preparation for detonation.
The present invention may also be used with a retrievable packer to circulate and displace the mud with a lighter fluid as the tubing-conveyed perforating gun is lowered into the well. The lighter fluid in the tubing string can be partially displaced by nitrogen to maintain an underbalance or pressure differential. The retrievable packer is then set to isolate the lower part of the well. There is now a light clean fluid extending from the firing head of the perforating gun throughout the tubing string to insure a sufficient impact of the detonator bar on the firing mechanism. The method and apparatus of the present invention accomplishes these objectives.
Method and apparatus which overcome the above drawbacks and provide the above desirable technique are the subject of the present invention.